PPFD

*** preface -- this stuff is meant to be a tool among other tools to optimally illuminate an area with your equipment. In the end you MUST observe and react to the plant and adjust. This will at best provide a good starting point that you can then make small patient adjustments without any "OH SHIT!" moments. So, some things seem precisely calculated, and they are, but you don't use them precisely, if that makes sense. This will speed up learning curve, it will not by an exact roadmap. you'd probably get there with trial and error within minimal difference without doing any of this math, but it will take longer for most. ***** Unless you have a quantum meter, that are quite expensive, you don't have a super accurate PPFD reading. the phone apps can still be useful, but expect +/- 10% or so? the CCT and SFD of the spectrum will impact % error. That's just using some 1-off conversion factor when one-size-fits-all is not applicable here so it most likely will be off a bit. Those apps don't measure photons, they measuer Lux then convert to PPFD. with how LED are made nowadays, it'll be good enough in most cases as long as you don't read it like it is "rule of law" Or, if you have honest specifications for your light the total umol/s produced relative to 1 m^2 will be very accurate provided it is a common sense distance above canopy for proper coverage of garden etc etc. if you'r area is larger than m^2, it obviousl reduces umol/s when converting to PPFD. if your area is smaller than 1m%2, then the conversion will result in a larger PPFD value than your umol/s. photons per meter squared is what we are after. you use a table for hours of use and PPFD provided. you would take multiple measurements in multiple locations equidistant from light and each other.. average those values out and that is your PPFD. i added the equation below, too. but google "DLI table" and even if columns of PPFD are not exact, the DLI given with nearest value is good enough, again, because these are ballpark concepts to be used along with plant observation. --- Heart of question asked: How much at different stages? well it varies due to different environmental conditions like temperature and RH% as well as ambient CO2 in atmosphere. But you can get a range. The recent article on GD has some suggestions for seedligns, vege and bloom etc.. but only use them as a ballpark idea and always observe and react to the plant. The biggest key to take from below is to start with less with younger plants, if seedling stretches too much, no matter what these values suggest, you need to increase PPFD. if it remains too small and nodes stack tightly on top of each other in an unhealthy way, you need less light (or less resulting PPFD, it's same thing). I edited this from the recent article to for better numbers... PPFD not dli, but you can convert with a table easy enough. i'll add a DLI for upper value on a 18/6 cycle or 12/12 as noted. 20/4 is fine, but you'll have to do some algebra. DLI is directly 1:1 proportional with hours of light. increase light by 10% and dli increases by 10%.. 2 hours more will need less light per hour in proportional manner. 18/6 light cycle Clone 100 - 150 -- 9.7DLI -- this just needs to be very weak.. if they droop, it neesd less light. After 7-10 days you have to start increasing light as roots form. Seedling 200 - 333 -- 21.6 DLI -- i think that's too low. probably get stetchy seedlings. i'd wager 333-400 is a better starting point for a recently sprouted plant. Vegetative 333 - 600 -- 38.9 DLI 12/12 light cycle Flowering 600 - 900 -- 38.9 DLI -- assumes 12/12 light schedule 18/6 cycle for auto in bloom Autos in bloom - 333 - 600 -- 38.9DLO See how once the plant is mature it can basically handle the same max DLI per 24 hours whether 12 horus or 18. Some common sense needed.. .you obviously should not try to supply 38.9DLI in 1 hour per day as that will burn the shit out of theplant, but in normal contexts of growing marijuana, max DLI is virtually no different whether over 12 or 18 hours... maybe some extra stretching is possible 12/12?? that's just a guess, but it's minimally different. Studies show yields don't change under 13/11 or 12/12 as long as same DLI given. a 6 hour different is potentially different, but can't be largely different. DLI = PPFD x .0864 x (hours/24) don't worry about the .0864 .. it's a comglomerate of other concerns that won't change for this context. Your lights physical structure will limit the space you can comfortably cover as much as any other attribute. Bar style frame may only radiate out 4-6" from end of frame.. more so in one direction than the other. (perpendicular to bars will be the longer spread). A rectangular QB will spread out further on the long side, and raising it up has limitations for spreading the light out for each frame type. 24-30" for early vege and further adjust. 18-24" for late vege / bloom. some are made to be close to the plant. Some lights need to be further away to reduce hotspsots in middle that could burn the plant. the more concentrated the light is, the more you have to raise it up to avoid hotspots. While not the answer you wanted, it's the logic to make all the decisions relative to your variables. in the end, you still have "some" trial and error ahead of you. Make some notes of what works best for each stage of life cycle... if you have seasonal changes, expect some variation by season. after 1 year, you'll have good notes for each season and you can start each grow with minimal adjustments to follow.